The following United States patents represent the closest known prior art U.S. Pat. Nos.: 3,076,431, 3,158,133, 3,158,134, 3,205,857, 3,297,020, 3,844,273, 3,948,249, 4,239,018, 4,247,758.
Since the advent of artificial insemination techniques, it has been possible to breed cattle to optimize characteristics such as size, milk productivity, disease resistance, and the like. However, although artificial insemination no longer requires the presence of the breeding bull at the time in insemination, it still requires that the farmer or rancher determine the exact time of estrus of a cow, so that the insemination will fertilize the cow. The accurate detection of estrus, or standing heat in cattle, is a problem long recognized but unsolved in the prior art.
A cow comes into heat approximately every 21 days, and then remains in heat for approximately 10 to 12 hours. The cow then ovulates approximately 14 hours after going out of heat. The time of ovulation is the optimum time for artificial insemination. If insemination is successful, the cow will not resume her cycles of heat until she calves at approximately 280 days after insemination. After calving, the ideal situation from the farmers standpoint is to reimpregnate the cow within 45 to 60 days after calving.
However, if it is not known when the cow first entered heat, the timing of the artificial insemination must be approximate, and a significant number of inseminations will fail to produce pregnancy. The farmer must then wait for the next estrus period to again attempt insemination. It is reliably estimated that it cost a dairyman three dollars per day per cow if the cow is not pregnant when it could be pregnant. In an average size diary herd of 400 cows, with an average calving interval of 14 months, accurate determination of standing heat could lower the calving interval to an average of 12.5 months. This savings of 45 days in the pregnancy cycle, multiplied by three dollars per day and by 400 cattle, can result in a net savings of $54,000 per year. Thus it is clear that the accurate determination of estrus onset in cattle is extremely important to dairymen, as well as other cattle breeders.
One type of device known in the prior art for detecting standing heat employs a dye or dye forming chemicals disposed in a frangible pack and secured to the base of the tail of each cow in a herd. With the onset of standing heat in any cow, the other cows will try to mount the one in heat, breaking the frangible pack and mixing and spreading the dye over the animal sufficiently to warn the cattleman that the cow has entered heat at some time since he last saw her. It cannot be determined to within 12-24 hours when estrus has begun, so that the timing of insemination involves too much guesswork and not enough certainty.
Another approach known in the prior art employs a temperature sensor placed in the vagina of the cow, and includes a radio transmitter which emits a signal when the internal temperature rises. This temperature gain may indicate onset of estrus, or may also indicate a fever due to bovine illness. This device has been tested only on virgin heifers at this time, and it is not known if it can be retained by an older cow with a more mature vaginal canal.
Another prior attempt to detect estrus involve a radio transmitter strapped to the leg of each cow and coupled to a pedometer. The theory is that a cow entering heat will take more steps per day than a cow not in heat. The radio transmitter transmits a signal to a computer which analyzes the number of steps taken by the cow each day. However, other factors may determine the number of steps per day. Such things as adverse weather conditions can cause an animal to become agitated and walk more, as can any circumstances that would somehow upset the cow.
A significant failing of all of these methods and apparatus, in addition to the shortcomings noted already, is that they do not determine the exact time that a cow has entered the standing heat cycle, and thus cannot provide the cattle owner with accurate information for optimal timing of artificial insemination.